Search

Erosion resistance of electrode materials is one of the key factors affecting the performance and working life of gap switches. In order to explore whether the electrode material with added nanoscale metalloid particles has better erosion resistance under the strong pulse current, a strong current discharge platform was built, and W80/Cu and W80/Cu–Al2O3 were selected as the research objects. The experimental study was carried out under a strong pulse current with a peak value of over 100 kA. By comparing the mass change, the microtopography, and surface roughness of the erosion area, it was found that the addition of nano-Al2O3 particles improved the erosion resistance of the W–Cu alloy. The anode loss was down about 14.7% slightly after adding Al2O3, and the cathode loss of W80/Cu–Al2O3 was down about half. The addition of Al2O3 will increase the working life by 25.3%. Besides, the microstructure of the erosion area became flatter and the roughness was reduced. [ABSTRACT FROM AUTHOR]

Based on the gas discharge theory involving distorted E-field enhancement, a physical model is proposed to estimate the switching delay for gas-insulated trigatron spark gaps with a trigger pin inside the main electrode. Two discovered breakdown modes, i.e., fast-breakdown mode (FBM) and slow-breakdown mode (SBM), can be unified in this model. Raether criterion can distinguish these two modes. If the main E-field and enhanced E-field near the trigger pin tip are great enough, FBM forms easily. Otherwise, if streamer development needs to rely on the second ionization process and relevant distorted E-field enhancement, the breakdown of the main gap would turn into SBM. The enhanced E-field near the trigger pin tip may affect the threshold main E-field of FBM. The distorted E-field enhancement may affect the switching delay length of SBM. [ABSTRACT FROM AUTHOR]

The polyamide 66 (PA66) fabrics are hard to be colored or glued in industrial production due to the poor hydrophily. Diffuse plasma is a kind of non-thermal plasma generated at atmospheric pressure in air. This paper proposes that large-scale diffuse plasma generated between wire electrodes can be employed for improving the hydrophily of PA66 fabrics. A repetitive nanosecond-pulse diffuse-discharge reactor using a cylindrical wire electrode configuration is presented, which can generate large-scale non-thermal plasmas steadily at atmospheric pressure without any barrier dielectric. Then the reactor is used to treat PA66 fabrics in different discharge conditions. The hydrophilicity property of modified PA66 is measured by wicking test method. The modified PA66 is also analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) to prove the surface changes in physical microstructure and chemical functional groups, respectively. What's more, the effects of treatment time and treatment frequency on surface modification are investigated and discussed. [ABSTRACT FROM AUTHOR]

A 700-kA gas switch with graphite electrodes for pulsed power supply module has been developed. This paper describes the design, construction, and testing of the high-current gas switch and its trigger system. The two-electrode gas switch is selected, which suffers high peak and fast rise time currents. The trigger generator based on resonant charging of a pulse transformer is constructed to trigger the gas spark. An electrodynamic force model of switch electrodes is established. The electrodynamic force of connecting wires is also calculated. By comparison of the mechanical strengths of polyformaldehyde, epoxy, and fiber-reinforced plastic (FRP) rods, where FRP rods are selected as switch rods, the experimental results show that the mechanical strength of the switch increases by 200%. Extensive electric testing has proven the operating parameters of the switch and its trigger system. The experimental results show that the measured discharge current waveform is demonstrated to be over a 700-kA peak current and a 500- \mu \texts pulsewidth. The transfer charge per shot is more than 500 C. [ABSTRACT FROM PUBLISHER]

Starting from the updated requirements of an advanced laser system, a switch–trigger system for a 2.0-MJ pulsed power supply (PPS) module is developed. This paper discusses the design, construction, and testing of this switch–trigger system. The two-electrode construction for the spark gap switch is selected because of its superiority in terms of long working life, high peak currents, and fast rise time of currents. The trigger generator based on resonant charging of a pulse transformer is constructed. A magnetic isolator and a pressure controller are the auxiliary equipment of this system. In the section based on mathematical principles, the equations of the lifetime and stability of this spark gap switch with graphite electrodes are given. These expressions can be regarded as the design basis of the same type of switch. As for the trigger generator, the analysis states that an appropriate ratio can be obtained when using the resonant charging based on a core-type pulse transformer. The charging time is dependent on the leakage inductance and the capacitance of the primary and secondary capacitors. Extensive testing proves the operating parameters of the switches and the trigger generator. The measured discharge current waveform of the 2.0-MJ capacitive PPS module is demonstrated to be over 500 kA peak current and 500 \mus pulse width. The life test proves that the switch–trigger system can support more than 200 kC transfer charge. By replacing the electrodes, the lifetime of this switch can be extended furthrer. [ABSTRACT FROM PUBLISHER]

The development of a three-electrode trigatron gap with the trigger electrode inside the main electrode is discussed in this paper. Two models of the operation mechanism are proposed to explain the breakdown in the trigatron gap. In addition, a mathematical model was proposed to calculate the breakdown time based on the theoretical analysis. The influence of different parameters on the breakdown time is discussed. Some characteristics in dry air have been experimentally determined such as the influence of the air pressure and the influence of the undervoltage ratio on the spark gap operation. The experimental results show that the operating voltage range between 0.5 and 0.7 might be reasonable. Then, the experimental results and analysis demonstrate that there are three regions divided by two inflection points, and the corresponding values of the undervoltage ratio are threshold values presenting different breakdown processes. [ABSTRACT FROM PUBLISHER]

The limited lifetime in a high current is the main drawback of spark-gap switches. Electrode replacement is an easily suggested method to extend the lifetime. In order to perform electrode replacement, thermal damage caused by heating effect should be prevented at the static electrical contact interfaces between the electrodes and the holders. Based on the Holm model, the Hertz formula, and the heat conduction theory, a mathematical model of the contact temperature rise is proposed in this paper. This mathematical model can prove quantitatively that the pulse-current integral (action integral), material physical properties, and mechanical characteristics of spark-gap switches are key parameters affecting the temperature rise. The action integral is determined by the electrical parameters. Material physical properties include the thermal conductivity, the specific heat, the density, the electrical resistivity, the elasticity modulus, and the Poisson ratio. Mechanical characteristics of spark-gap switches include the contact radius/area, the contact force, and the contact surface roughness. The implementation of electrode replacement depends on the reasonable configuration of these key parameters. The experiments in a 1.2-MJ power supply module give that the phenomenona correspond with our analysis. Based on the analysis in this paper, an electrode holder structure is proposed as a practical solution for extending the useful lifetime of spark-gap switches with graphite electrodes. [ABSTRACT FROM PUBLISHER]

High-power closing switches with graphite electrodes have been used in power-supply system for a large laser pump. The useful lifetime of this kind of switch is an interesting and important issue. Previous researchers have observed that the graphite erosion loss is proportional to the amount of transfer charge in a high-power pulsed discharge. Therefore, the erosion rate of graphite may be used for predicting and estimating the electrodes' useful lifetime. According to the mathematical model proposed in this paper, the lifetime of a closing switch with graphite electrodes is dependent upon several key parameters, including the dimensions of electrode, density, the erosion rate of graphite electrodes, undervoltage ratio, working temperature, and the amount of energy transfer. A mathematical formula describing the relationship between lifetime and those parameters has been deduced. Based on a newly developed spark-gap switch which can support over 100-C single transfer charge, this proposed lifetime model has been verified. This paper may quantitatively perform the function of guidance in engineering applications of graphite electrode switches in large pulsed-power facilities. [ABSTRACT FROM AUTHOR]

A spindle-shaped diffuse plasma cage is represented by photoreportage in the room-temperature atmospheric-pressure air. It is found that a closed plasma cage covered with diffuse plasma can be obtained only in an appropriate ring-ring electrode distance. By adjusting the ring-ring distance, we can destroy the closure property characterized by the appearance of corona or arc discharge on the surface of the cage. In addition, much larger plasma cage can be acquired using larger rings or adding more rings. [ABSTRACT FROM PUBLISHER]

The impact of the wire length on the large-scale diffuse discharge is investigated. The images and electrical measurements show that for a nanosecond pulse with a long tail, the decrease of the wire length can result in the transition from a diffuse mode to a spark discharge. [ABSTRACT FROM PUBLISHER]

This paper illustrates an observation of large-scale cold plasma generated by repetitive nanosecond pulses and barrier-free wire electrodes in atmospheric air. The length of plasma tape achieved 110.0 cm and can be further lengthened. The applied repetitive nanosecond pulses are with \(\sim 30\) -ns rise time, negative \(\sim 70\) -kV peak, and \(\sim 750\) -ns width at the 500-Hz repetition frequency. The discharge images indicate that the large-scale homogeneous nonthermal plasma in open air can be stably formed with appropriate conditions. [ABSTRACT FROM PUBLISHER]

Analysis of breakdown mechanism in gas-insulated trigatron switches is important for the engineering design and function prediction. Based on the gas discharge theory, a physical model was proposed to estimate the breakdown time for gas-insulated trigatron switches. And the model can explain the breakdown in the trigatron switches with two modes of the breakdown mechanism, i.e., fast breakdown mode (FBM) and slow-breakdown mode (SBM). Based on Raether breakdown criterion, this paper discussed the factors affecting on the E-field enhancement. The E-field is composed of the static E-field and the dynamic E-field, which leads to transformation of breakdown mechanism. Some coefficients could be determined by experiment and simulation, which are helpful to get the quantitative solution of breakdown time. [ABSTRACT FROM AUTHOR]

Working characteristics of a three-electrode trigatron spark gap is discussed in this paper. Breakdown probability is proven to fit a Weibull distribution. For an engineering application, the lower limit of undervoltage ratio depends on breakdown probability, and the upper limit of undervoltage ratio depends on self-breakdown probability. Some characteristics have been determined experimentally, such as the influence of the air pressure and the influence of the undervoltage ratio on spark gap operation. Curve fitting and quasi-data mining are good methods for research on triggering characteristic in the paper. Therefore, a maximum operation range curve and a boundary line of expected delay time could be determined by application requirements, theory calculation, experimental data and curve fitting. On this basis, optimization operation range could be obtained, which represents a preferable performance of breakdown with expected delay time. It may provide guidance for engineering application. [ABSTRACT FROM AUTHOR]

In a high-power laser facility with multiplex power modules, the dispersion of self-breakdown voltages of spark gap switches might result in a so-called pre-fire problem. Pre-fire probability of spark gap switches with graphite electrodes must be constrained at extremely low level. In this paper, Pedersen model was used to explain the causes of pre-fire. The microscopic surface roughness of worn graphite electrodes had a major impact on pre-fire. And this paper had deduced the cumulative probability distribution of pre-fire, and given a relevant Weibull distribution equation. Several typical graphite materials were tested too. The experimental results revealed that electrodes should use graphite with higher hardness, smaller particle size and greater flexural strength. This was consistent with the analysis of Pedersen model. More significantly, based on the experiments of typical graphite materials, two Weibull constants of the cumulative probability distribution of pre-fire were obtained by a graphing method. Therefore, it is possible to calculate, reduce or control the occurrence of pre-fire in a facility with many gas switches. Via optimizing the operating under-voltage ratio of multiplex switches, the expectable pre-fire probability can be achieved. [ABSTRACT FROM PUBLISHER]

Electrode replacement is an effective method to extend the useful lifetime of the spark gap switch with graphite electrodes. In order to perform electrode replacement, suppressing temperature rise and preventing static welding/erosion should be considered for the static electrical contact interface between the electrode and the holder. In this paper, a mathematical model of contact temperature rise is proposed based on the Holm model and heat-conduction equations. This mathematical model can quantitatively prove that some material properties of the metal holder and some mechanical characteristics of the spark gap switch are key parameters affecting temperature rise. Material properties of the metal holder include thermal conductivity, specific heat, density, electrical resistivity, elasticity modulus, and the Poisson ratio. Mechanical characteristics of the spark gap switch include contact radius/area, contact pressure, and contact surface roughness. Optimum configuration of these key parameters reduces temperature rise and prevents static welding/erosion. [ABSTRACT FROM AUTHOR]

In a high-powered single pulse system, the graphite electrode is better than other common metal electrodes for high energy transfer and pulse discharge. In this paper, the erosion mechanism of graphite electrode is investigated with the thermodynamics theory and the experimental results. Based on a simplified mathematical model, the graphite electrode erosion process of high-powered spark gap switch is also analyzed. The analysis results show that the relationship of the graphite electrode erosion and the charge transfer is linear, which is accordant with the experimental results. [ABSTRACT FROM AUTHOR]

A large-area and periodically patterned nanoporous aluminum grid with controlled pore size was fabricated by poly(ethylene oxide)-assisted self-assembly of polystyrene nanospheres. The grid layer was used as the shadow mask for the creation of nanochannels in a polymeric dielectric layer, as well as the base electrode in a space-charge limited transistor prepared thereafter. A high performance device with poly(3-hexylthiophene) as conducting semiconductor was achieved, yielding a high on-current output of ∼12 mA/cm2 and a high on-off ratio of ∼2 × 104 at a collector voltage of -2.0 V. [ABSTRACT FROM AUTHOR]